<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<div id="container">这是container</div>

<button id="btn">替换</button>

<body>
    <script src="/js/index.js"></script>
</body>

</html>